To avoid being pick-pocketed, keep your wallet in your front pocket, especially a pocket that can be buttoned up. Best of all, use the inside pocket of your coat or jacket. There are also a load of different “ money belts” that either hang inside your shirt or wrap around your waist (under your shirt), etc.
It should not be obvious you are wearing one, and do not try to access it and show people where you keep your money get your money out of a money belt in secret. Make sure it's waterproof because travelling can often be sweaty/perspiring work.
Please do not use the bum bag/fanny pack varieties there is no better way to advertise the fact that you have a load of valuables on you, and, of course, they were never cool.